In my own mind I've devised two ways of playing slap. One I can do fast, and the other I can do slow. Here goes:

1: Simple Slap. This is the basic thumb/finger routine done on a 1-2-1-2-1-2 rhythm. Usually played on quaver/eighth notes. Play fast on octaves for a steretypical Flea sound.

2: Hard Slap (good names, eh?). This is where you slap the lower string, pop the higher string, then slap the lower string again, but this time muting. As far as I know this is proper slap, but is very hard. Normally it's done using a 1-2-3 feel. Twelve notes played in each bar, in a 4/4 time signature.

Comments?

Sorry to burst your bubble, but those are variations of basic octave and triplet techniques.
They're just the starting point.

Check out Mark King if you want to hear alot of this used and what you can do with it if you combine the different techniques and variations. There are a few mp3's out there I recommend :

Mark King - Bass - Slap Lesson (Guitarist Magazine).MP3

Mark King - Bass!.mp3(also called Bass instruction)

Also Level42 - Mr. Pink.mp3

almost every slap bassist uses these patterns .. Mark King is just one of my favorites. Later.

If you wanna know other slapping techniques, then check out Victor's Wooten's video Super Bass Solo Technique. It goes over his Double Thumping Technique (a very useful slapping technique at times). Hope this helps!

Or check out Bill Dickens' videos.
Serious slapping frenzy from the Buddah of Bass.

Thanks all. I'm sort of a 'starting' slap player. Working it out for myself really, so I'm not pretending to be the best slap player ever born, in fact I'm fairly useless. I pretty much play a constant bass note and vary between a 6th, b7th and 8ve on the higher string. Simple but I guess it's good practice. I know it's extremely simple, but I'm still trying to get the hang of the mutes thing - otherwise it all seems a bit 'empty', don't you think?

I've been 'slappin' for a good while now and I got the hammer and pluck down, now I'm tryin to get the mutes down. My goodness! It's gonna take another good while til' I get the hang of that! It seems like the things that I love to do are no walk in the park to get good at! :)